Molecularly cloned human sequences related to the tyrosine-specific protein kinase domain of the transforming gene of Gardner-Rashee feline sarcoma virus (GR-FeSV) were shown to represent the c-fgr (human) proto-oncogene. Restriction endonuclease analysis of human DNA revealed that c-fgr (human) was distinct from sequences homologous to the oncogenes v-yes and v-src which encode a produce closely related in predicted amino acid sequence to that of v-fgr. The c-fgr (human) proto-oncogene was localized to human chromosome 1 bands p36.1-36.3. The c-fgr gene was shown to be expressed in certain normal human tissues. In order to study the molecular pathogenesis of lentivirtus diseases of mammals, the genome of caprine arthritis and encephalitis (CAEV) virus was moleculary cloned and characterized. Southern analyses delineated the genetic relationship of CAEV to other retroviruses and also indicated that a variety of mammalian species do not harbor sequences homologous to CAEV with their genomes. The in situ chromosome hybridization technique was used to map the sites of residence of H-ras, K-ras and N-ras within the human genome in greater detail. A survey of human urinary tract rumors provided information regarding the frequency of the occurence of activated ras oncogenes and their associated molecular lesions. Human DNA sequences corresponding to a new human oncogene isolated by A. Eva were recovered from a library of normal fetal liver DNA. These sequences are being characterized structurally in order to determine the mechanism of activation of this gene during the neoplastic process.